1. Field
Embodiments of the present invention relate to an engine throttle control system. More specifically, certain embodiments relate to an engine throttle control system that can obtain linearity of an amount of change in engine output relative to an amount of change in operation of a throttle operating device.
2. Description of the Related Art
Some conventional engine throttle control systems include an idle air control valve (IACV) that controls an intake air amount of an engine by use of the idle air control valve (see Japanese Patent Application Publication No. Sho 61-294152). The IACV might be provided in a bypass passage communicatively connecting an upstream and a downstream of a throttle valve. In an engine having such a throttle control system, although the intake air amount during an idle operation is controlled by use of the control valve, an intake air amount corresponding to a throttle operation by a driver is controlled by the opening and closing of the throttle valve.
A throttle control system of a so-called throttle-by-wire system (hereinafter, referred to as a “TBW system”) detects an operation amount (operation amount from zero) of a throttle operating device (an acceleration pedal or a throttle grip) as an electrical signal by use of a sensor. This throttle control system controls the opening degree of a throttle valve in accordance with the detection signal.
Japanese Patent Application Publication No. Hei 11-13516 (JP '516) describes a throttle control system of the TBW system. The throttle control system described in JP '516 selects a larger one of a target intake air amount calculated on the basis of an acceleration opening degree and an engine speed, and a target intake air amount with load control at deceleration. The throttle control system then calculates a target throttle opening degree on the basis of the target intake air amount thus selected. The throttle control system employs a technique described below in order to eliminate a failure in which, because of a difference between a selected target intake air amount and a target intake air amount corresponding to a torque requested by the driver, a change in the driver's request is not reflected in an output when the selected target intake air amount is large. Specifically, the throttle control system acquires a target torque by adding the driver's requested torque and an engine request torque different from the driver's requested torque, and then determines a target intake air amount on the basis of the target torque.
According to the control system of the TBW system described in JP '516, it is possible to reflect a driver's request within a small throttle opening region in a change in output. However, suppose the simply adding of a throttle opening degree required for the idle operation and a throttle opening degree corresponding to a driver's requested torque, that is, an operation amount of the throttle operating device, in a case where the opening degree of the throttle enters in a middle or large opening region. In this case, a stable correlation between an intake air amount and an operation amount of the throttle operating device, namely, a throttle linearity may not be obtained. To put it differently, the intake air amount sometimes varies even with the same operation amount of the throttle operating device due to the magnitude of the throttle opening degree required for the idle operation.